Manufacturing processes of high-voltage cables require that the cleanliness of the material is preserved from initial production to cable extrusion. To this end, it is important that the material remains in a closed system throughout the whole process. A critical moment occurs when a bag or a box with fresh pellets, raw material, has to be connected to the hopper of the extruder for unloading. The bag or box has to be opened in some way or another and the spout of the bag connected to the hopper of the extruder. At this moment, special care has to be taken in order to prevent pollution of the raw material with dust or other carton residues form the transport box falling into the feed opening, or with other contaminants. The raw material may for example pellets of polyethylene used for producing insulation to an electrical cable.
The conventional methods and arrangements for unloading raw material into a hopper of an extruder require considerable manual handling and intervention for connecting the unloading spout of the box or bag to the hopper of the extruder. These manual operations have to be done in clean room atmosphere and such that contamination of the raw material is prevented. The prior art methods usually comprise following manual steps: placing the raw material bag above the feed inlet of the hopper of the extruder, cutting open the seal of the discharge spout of the bag, removing the lid of the feed inlet, connecting the bag to the feed inlet of the hopper and starting the unloading of the raw material by opening a adjusting a tie provided to the discharge spout of the bag. When the unloading is completed the following steps are carried out: adjusting the tie for closing the discharge spout, disconnecting the discharge spout of the bag from the feed inlet of the hopper and closing the lid of the feed inlet.
The problem with these prior art methods and arrangements is that they require considerable amount of manual work. The manual handling on the other hand causes risks that contaminants may get into the feed inlet of the hopper. Thus the prior art arrangements do not provide efficient means for preventing contaminants from getting into the feed inlet.